This invention relates to a video camera device, in which a camera head and a signal processing unit are provided as separate components and connected to each other by a signal line.
As such a video camera device, there is an endoscope device which is disclosed in United States patent application Ser. No. 914,168, filed Oct. 1, 1986. The device comprises a solid-state image sensor device, e.g., a charge-coupled device (CCD) for picking up an image of an object. The CCD is provided at a distal end of an endoscope as a camera head. For size reduction of the distal end of the endoscope, a signal processing unit for processing the output of the CCD is provided separately from the endoscope. Usually, it is provided in a light source unit. A drive pulse signal for driving the CCD is transmitted from a drive pulse generator provided in the signal processing unit to the CCD through a signal line included in a cable connecting the endoscope and light source unit. An output of the CCD is transmitted through the signal line from the endoscope to the signal processing unit, undergoes such processing as clamping and sampling/holding, and is changed into an image signal of the object.
The drive pulse signal is a high frequency pulse signal. Therefore, if it is transmitted through a long signal line, its waveform is distorted during transmission. In this case, when it is supplied to the CCD, it is no longer a pulse wave, so that the CCD can not be driven with accurate timing. For this reason, a matching circuit for compensating for the waveform distortion should be provided in the signal processing unit for supplying the drive pulse signal to the CCD through the matching circuit.
The output of the CCD also is delayed while it is transmitted to the signal processing unit, and when it enters the signal processing unit, it is delayed with respect to the timing of the drive pulse signal. Therefore, the signal processing unit can not clamp or sample/hold the transmitted signal at a proper timing. In order to compensate for this, various timings of the signal processing are delayed with respect to the timing of the drive pulse signal in accordance with the kind of the endoscope (i.e., the length of the signal line).
Generally, the cable is integral with the endoscope and the length of the endoscope varies with the kind thereof (i.e., the object to be examined). Therefore, the length of the signal line between the CCD and the signal processing circuit is varies in accordance with the kind of the endoscope. In order to commonly connect a plurality of endoscopes to a common signal processing unit (light source unit), therefore, it is necessary to provide the signal processing unit with timing matching circuits corresponding in number to the number of endoscopes of different kinds but commonly connected to the signal processing unit. This means that the size of the signal processing unit is increased with increase of the number of timing matching circuits. Further, since the amplitude of the drive pulse signal is considerably large and the high frequency drive pulse signal has many higher harmonic wave components, the influence of electromagnetic wave, which is radiated from the signal line as the drive pulse is transmitted from the signal processing unit to the CCD, can not be ignored.